Three quarters of osteosarcomas occur in the long bones of the legs, and another 10% in the arms.

The researchers suggest pre-cancerous genetic changes occur in the bone tissue during childhood and that during periods of rapid growth in teenagers further genetic damage occurs, turning these cells cancerous.

A similar pattern is also seen for Ewing sarcoma, which they said may be caused by related factors.

'Clues'

Incidence of testicular cancer, which is usually a germ cell cancer whatever the age of the patient, is known to peak in young adults.

In contrast, ovarian cancers tend to peak in the over-60s. However, the Manchester team's research showed germ cell tumours of the ovary are most frequent in older teenagers.

Germ cell tumours in the brain also disproportionately affect this age group.

Hormonal and other factors affecting growth and development before and after birth could affect their development, the researchers said.

The Epstein-Barr virus has already been suggested as a cause for Hodgkin lymphoma, but the researchers suggest other infectious agents may also cause the cancer.

Development factors

Professor Jillian Birch, Cancer Research UK Professorial Fellow at the University of Manchester led the study.

She said: "These can be regarded as 'true' teenage and young adult cancers that typically occur specifically in this age group.

"Having identified the very specific types that are teenage and young adult cancers, we are able to find clues as to why this age group gets cancer.

"These point to infections, adolescent growth spurts, hormones and other growth and development factors as among the most probable causes."

Experts said exposure to chemicals during development in the womb and childhood was one potential cause that was also being considered by researchers.

Professor Tim Eden, appointed as the UK's first professor of teenage cancer by the Teenage Cancer Trust, said: "These patients might be very susceptible to something which might be safe for the rest of the population."

Researchers are particularly interested to see if exposure to tobacco smoke, either through their own or passive smoking, could increase the risk of cancers in the young, though not necessarily lung tumours.